The invention relates to a process for the liquid phase hydroconversion of charges containing heavy fractions, particularly heavy hydrocarbons and more specifically relates to their deep conversion.
Non-catalytic processes exist and among these a process described in U.S. Pat. No. 4,292,168 uses a hydrogen donor solvent at 350.degree. to 500.degree. C. and under 2 to 18 MPa. It is possible to choose as solvents pyrene, fluoroanthene, anthracene, etc., their nitrogen derivatives, their hydrogen derivatives and their short-chain alkyl derivatives. The latter non-catalytic process operates well in the case of moderate conversions. However, when it is wished to reach higher conversion levels (beyond 50%) and even deep conversions (beyond 70%), the conditions are more severe and then larger coke quantities form.
The prior art describes at length (e.g. in U.S. Pat. No. 4,134,825) that unlike in the case of supported catalysts, finely divided catalytic species obtained from a precursor, in the form of a metal complex soluble in an aqueous, alcoholic or organic medium, are able to ensure the hydroconversion under satisfactory conditions without being limited by deactivation and poisoning phenomena encountered with conventional catalysts.
Thus, in the past, it has been possible to obtain under hydrovisco reduction conditions in the presence of this type of catalyst up to and exceeding 50% conversion of heavy fractions into lighter fractions without excessive coke formation. However, as a function of the nature of the charges, the performance characteristics often remain limited in the deep conversion range.
One means for improving the performance characteristics is to operate in the presence of a larger catalyst quantity, but then the costs are higher. Another means is to significantly increase the hydrogen pressure, which involves the use of specially adapted and expensive equipment. One aim of the invention is to avoid the use of such catalyst quantities and such hydrogen pressure levels for obtaining better performance characteristics.